Avoid N^2 walk placing renderers when building the render tree

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 0620531f3449e3f1339a7051bcd1b19214ebf09d..94ebf032be0e4d2f1613456c76352557ecf3a6ec 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -1663,7 +1663,7 @@ void Document::recalcStyle(StyleChange change)
                 renderer()->setStyle(documentStyle.release());
         }
 
-        for (Node* n = firstChild(); n; n = n->nextSibling()) {
+        for (Node* n = lastChild(); n; n = n->previousSibling()) {
             if (!n->isElementNode())
                 continue;
             Element* element = toElement(n);